This invention relates to an electrostatic separator and to a method of employing the same wherein the separator produces different electrical fields for attracting and for repelling materials being separated.
It is well known that electrostatic charges may be produced on surfaces and that these charges will be attracted to or will attract other materials having the opposite charge. This principle has been applied in the past to produce apparatus and methods for separating dust particles from a gas stream or from a solid surface and for separating particles having different electric properties. These teachings all involve the separation of charged particles. In the separators of the prior art a drum or a plate is charged and the materials to be separated are placed close to the charged surface permitting the particles that are to be separated to migrate to the charged surface. In another type of separation neutral particles are separated in a non-uniform electric field; for example, the field between a curved surface and a flat surface. In such a nonuniform field the particles are moved toward the more intense portions of the field and in this fashion separation between particles of different dielectric properties can be obtained.
There are many references in the prior art relating to the separation of particles, and an important work in the field is Dielectrophoresis, Cambridge University Press, 1978. In such work a detailed treatment of the separation of neutral particles in a non-uniform field can be found, as well as the use of elements or grids to inhibit bunching of such particles. Also, various other methods and apparatus employing such particle separations may be found in U.S. Pat. Nos. 2,317,210--Masse; 4,100,068--Jordan; and 4,226,703--Stout; and British Pat. Nos. 218,354 (1924) and 1,026,438 (1966). None of these prior art references either alone or in any appropriate combination suggest or teach the invention disclosed and claimed herein or in any way to alleviate the inherent problems and deficiencies in such prior art, as will be apparent from a full consideration of this specification.
It is an object of the present invention to provide a multifield separator, i.e. one having multiple charged zones available to assist in the separation. In the multifield separator there are one or more zones where the field is generated by a charge, and another zone or zones where the charge is of the opposite potential. When these zones are employed on the same separator it is possible to achieve an efficient separation by attraction of polarizable particles and then repelling such particles from the surface and cleaning of the surface of any remaining particles which were not repelled off such surface; and all of this accomplished in a single continuous movement. It is therefore an object of this invention to provide a multifield separator which will attract particles at one zone of the separator and repel the same particles at another zone of the separator. Still other objects will appear from the more detailed description of this invention given below.